The invention relates to a ram-side ejector device for workpieces in single- or multi-stage presses, said presses comprising a press carriage, which is movable between a pressing position extended relative to a stationary press die and an end position at a distance therefrom and comprises a press ram cooperating with the stationary press die, further comprising an ejector pin carried on the press carriage in the pressing direction and penetrating the press ram, said ejector pin being movable between a retracted end position, in which said pin is supported, by its end remote from the die, on a stop formed on the press carriage, and an extended position protruding from the press ram, wherein the end of said pin remote from the die is distanced from the stop, said pin being provided with a resetting means acting counter to the direction in which said pin is extended and which may be releasably blocked, when the press carriage returns from its pressing position, by a blocking means fixed to the press frame counter to the return movement of the press carriage, the activation or deactivation of the blocking means and the activation of the resetting means being program-controlled and coupled with each other.
Such ejecting devices serve to eject workpieces on the ram side of single- or multi-stage presses, such workpieces including in particular screws, bolts, rivets or similar parts. The ejecting operation is integrated in the press operation cycle.
Devices for generating a ram-side ejection movement after the pressing operation in order to release and eject workpieces from the tools, e.g. from hexagon-head rams on automatic shaping presses, have long since been known. For this purpose, a movement is initiated from outside, i.e. either from the press frame (e.g. DE 24 50 631 C) or from the crankshaft (e.g. DE 1 750 033 C) into the press carriage of the shaping press, wherein the desired ejection movement is then generated via cam plates, angle levers or other transmission elements. However, these known ejector systems have the disadvantage that they are provided, in many cases, with many joints, levers, gearwheels and the like, and have a considerable mass which is to be moved together with the press carriage and is thus excited to vibrate. Moreover, these known ejector systems also have a certain stroke which causes the workpiece to be released first from the stationary die of the shaping press before being released from the moving ram of the press, which may result in the workpiece being lost before it can be securely taken, for example, by the gripping fingers of the transfer device of the press. A further disadvantage is that a change in the law of motion of the press carriage, for example when the carriage stroke changes, also requires a cumbersome change in the law of motion of the ram-side ejector, with the ejection stroke being changeable, in most cases, only with great effort.
As an overload safety device, the known ejector systems are usually provided with a breakage safety device which has to be renewed after being triggered.
Further, DE 100 07 255 A discloses a ram-side ejector device wherein an ejector lever can act upon the end of the ejector pin remote from the die, said ejector pin penetrating the ram, with the end of the ejector lever acting upon the end of the ejector pin being interposed between the latter and a stop on the press carriage and continuously contacting the end of the ejector pin remote from the die, even upon the return of the press carriage after the pressing operation. The return movement of the press carriage, the ejector lever is fixed in its position, immobilized relative to the frame, by means of a toggle connection and by an activatable solenoid such that said solenoid urges the ejector lever out of the press ram for the ejection movement during the return movement of the press carriage. Only if the desired ejection movement has been performed by the ejector pin, i.e. once it has been moved into the desired, fully extended position, the blocking of the ejector pin in its position fixed relative to the housing is eliminated by deactivating the solenoid. At the same time, the resetting means is activated, by which the ejector lever is retracted into the press carriage again and, thus, the ejector lever having its end contact the end of the ejector pin remote from the die is simultaneously tilted until it contacts the stop fixed relative to the housing. This return movement of the ejector lever is further supported by a spring prestressing it in this direction.
The toggle connection of the ejector lever, which is tiltably supported on the press frame, is simultaneously usable as an overload safety device which responds in order to protect the shaping press if the force by which the workpiece has to be urged out of the ram by means of the ejector pin exceeds a preadjusted level, for example upon tool breakage. The toggle lever system then bends in, because the programmably adjusted holding force of the solenoid is exceeded, which can be recognized by the program control of the shaping press enabling immediate stopping of the press. Thus, a renewal of the breakage safety device as required in the previously known ejector systems is not required in this case.
By the programmable selection of the switch-off time of the current supply to the solenoid during the return movement of the press carriage, the time period during which the ejector pin is immobilized, and thus the ejector stroke, may be easily predetermined, so that each ejector pin of multi-stage presses may be individually adjusted via the program control of the press. The cumbersome change of the law of motion for the ram-side ejector upon a change in the law of motion of the press carriage required in previous ejector systems is thus dispensed with.
While this known ejector device already essentially solves problems of previously known ejector devices in an excellent manner, it still suffers from relatively large masses of the system due to the ejector lever employed and its toggle lever connection comprising the solenoid blocking mechanism on the press frame, and it is, thus, not usable at higher operating speeds of the press (approx. over 50 pressing operations per minute).
In view thereof, it is an object of the invention to improve such ejector device in such a way that the total mass of the ejector system can still be reduced further and that, in particular, use thereof is possible also at higher press speeds in the range of over 50 press strokes per minute.